From time to time, it may be possible for an engine of a hybrid vehicle to stall during engine starting. The engine stall may be due to poor air-fuel mixture preparation, fuel properties, or other engine operating conditions at the time of engine starting. One way to determine if an engine has stalled during engine starting is to monitor engine speed. If engine speed declines so less than a threshold speed, it may be determined that the engine has stalled to that the engine may be restarted. However, if the engine is coupled to an electric machine that is propelling the vehicle, the electric machine may rotate the engine such that an engine stall may not be detected simply by monitoring engine speed. For example, an engine may be started via closing a driveline disconnect clutch that links the engine to an electric machine that is propelling a vehicle. The engine may stall as torque provided by the electric machine accelerates the engine up to the speed of the electric machine. The engine speed may continue to increase due to torque provided by the electric machine. As such, the engine's speed may not be indicative of an engine stall condition. However, an amount of energy consumed by the electric machine may be increased to maintain engine speed without producing useful work. Therefore, it may be desirable to provide a way of determining whether or not an engine has stalled when the engine is coupled to an electric machine that propels a vehicle.
The inventors herein have recognized the above-mentioned issues and have developed a vehicle operating method, comprising: indicating an engine stall in response to a request to determine a presence or absence of the engine stall when the first engine torque is less than a second engine torque, the first engine torque based on a torque converter impeller torque and a motor torque; and opening a driveline disconnect clutch in response to indicating the engine stall.
By indicating an engine stall condition responsive to a first engine torque being less than a second engine torque, it may be possible to determine an engine stall condition when engine speed may not be indicative of an engine stall condition. For example, if an engine is attempted to be started via torque produced by an electric machine that is propelling a vehicle, an engine stall may be determined even though engine speed may be increasing. In one example, the engine stall may be based on comparing a first engine torque estimate against a second torque estimate. Thus, the engine stall condition may be determined independent of engine speed. If an engine stall condition is indicated, mitigating actions may be taken via an engine controller.
The present description may provide several advantages. In particular, the approach may determine whether or not an engine is stalled even if the engine is rotating at a same speed as an electric machine that is propelling a vehicle. Further, the approach may be provided without additional engine sensors or actuators. Further still, the approach may reduce energy consumption if an engine stall occurs.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.